This invention relates to spectrophotometers for the measurement of color and appearance of objects. More particularly, this invention relates to handheld portable spectrophotometers for remote measurement of color and appearance of objects.
Spectrophotometers are generally used to measure the color or appearance of objects, for example, paints, plastics, textiles, and to analyze powdered chemicals or biological specimens. Such color measurement may be used to formulate or adjust the mixture of colorants. Spectrophotometers measure the diffuse reflectance factor, which is defined as the ratio of light flux reflected from the sample to be measured to the light flux incident upon the sample and as compared with a "perfect white diffuser".
Most current spectrophotometers are tabletop instruments weighing in excess of 50 pounds and are generally connected to a personal computer for computation and analysis and operator control and display. The weight and size of the spectrophotometer results from the stability requirements of the internal optical system to maintain precise and consistent measurement of color. Operation of the spectrophotometer is also usually restricted to a limited range of operating temperature.
Accordingly, samples must be brought to the spectrophotometer to be measured for their color or appearance, necessitating, in some cases, taking a "swatch" or a piece of a very large object to a laboratory for color analysis. The computation complexity involved in the reformulation of colorants necessitates the use of a modern personal computer with the spectrophotometer for such analysis.
Some portable spectrophotometers have recently been developed but, while satisfying the portability requirement, such spectrophotometers fail to meet other important criteria. For example, temperature and mechanical shock sensitivity limit their ability to make accurate color measurements. Additionally, the computational power of such portable spectrophotometers is limited to mere measurement and display of color information with no analysis and correction of colorants, often referred to as "color matching". Color matching includes, by way of example, match prediction, batch corrections, tinting strength calculations, and retrieval of closest color shades from a shade library. Further, because of their box-like rectangular form, such portable spectrophotometers cannot access recessed or height-restricted environments such as the dashboard near the windshield of an automobile.
Accordingly, there exists a need for a portable spectrophotometer having the ability to access restricted environments and sufficient computational power for complex calculations of color measurement and colorant formulation.